Method of flame spraying and powder



United States Patent Office 3,372,054 Patented Mar. 5, 1968 Thisinvention relates to the flame spraying of metal powders upon metalsurfaces, and it more particularly relates to the simultaneous sprayingand bonding of such coatings.

It has been customary in flame spraying metal powders upon metalsurfaces to utilize particle sizes finer than 100 mesh and preferably150 mesh and smaller. Nominal 150 mesh particle size powders normallyincorporate a distribution of finer particle sizes ranging down to 325mesh with a minor percentage of even finer. These fine powders have beenconsidered necessary to insure sufficient heating during passage throughthe flame to bond with the preheated metal surface upon which they areimpinged. The alloy compositions suggested for such powders have meltingtemperatures ranging approximately from 360 F. to 2200 F. They includelower melting temperature metals and alloys such as lead, aluminum,bronze, brass, silver base alloys, zinc, cadmium and the various nickeland cobalt base alloys in the upper portion of the aforementioned rangeand primarily between -l800 'F. and 2200" F.

The metals and alloys in the lower portion of the abov; range and belowl800 F. are highly susceptible to volatilizing and fuming when sprayedin the fine particle size previously deemed essential. This fumes awaycritical constituents to the detriment of the deposited coating. Thefumes of certain of these volatile metals such as lead, zinc and cadmiumare also highly toxic and are liable to poison an operator.

Alloy compositions in the higher melting temperature range from 1800 to2200 'F., when sprayed in the heretofore conventional fine particlesize, are highly sensitive to particle size and distribution andconfiguration. Deviation from prescribed particle size distribution islikely to interfere with the deposit of suitable coatings, and particlesof spherical shape are recommended for optimum results. This makes suchpowders difiicult to prepare and quite expensive.

An object of this invention is to provide a method and powder for flamespraying that minimizes the elfect of particle size distribution andconfiguration and any tendency of the powder composition to volatilize.

Another object is to provide such a method and powder that flame sprayvolatile metal powders without fuming.

In accordance with this invention the particle size of approximately75100% by weight of metal powder compositions having meltingtemperatures ranging approximately from 360 F. to 2200 F. is maintainedapproximately between -60 to +100 mesh passes through and is retained).The remainder of the powder may be of smaller or larger particle size nogreater than 40 mesh, and a particularly effective particle sizedistribution is as follows.

mesh.

Mesh size: Example in percent by wt. 40 +60 1 60 40 -80 50- 100 9 Theamount less than 100 mesh is predominately mesh.

This powder is flame sprayed upon a metal surface within an oxy-fuel gasflame to plasticize the powdered metal without volatilizing it. Theplasticized powder is impinged upon the preheated metal surface withwhich it coalesces and bonds to form a smooth continuous coating.

This invention, for reasons that are not completely understood,remarkably minimizes the effect of particle size distribution andconfiguration and any tendency of the powder composition to volatilizeto such an extent that such effect and tendencies are eliminated for allpractical purposes. Relatively economical and easily prepared powderscan thus be efficiently sprayed at remarkably high recovery rates in anysize distribution within the recited range and in any particleconfiguration-angular, spherical or otherwise. The prevention of fumingis highly important with metals that melt in the range of from 360 to1800 F. because many of them such as lead, aluminum, zinc and cadmiumare highly subject to volatilizing,

and the fumes of lead, zinc and cadmium are toxic. The

flame spraying of volatile metal powders without any loss of criticalconstituents from the ultimate coating or-emission of poisonous fumes isthus remarkably facilitated.

A particularly effective torch 'for'use in conjunction with thisinvention is of the general type described in a copending, commonlyassigned application for US. Letters Patent entitled Flame SprayingTorch, S.N. 297,844, filed July 26, 1963, now Pat. No. 3,220,068. Foreffectively performing the method of this invention, such a torchutilizes acetylene as the combustible gas, supplied at a pressureranging approximately from 2 to 14 p.s.i. and preferably from 8 to 12p.s.i. Oxygen is most efficiently used as the combustion supporting gas,supplied at a pressure ranging approximately from 16 to 50 p.s.i. andpreferably from 24 to 32 p.s.i. Highly efficient supply pressures ofacetylene and oxygen are respectively 9 p.s.i. of acetylene and 28p.s.i. of oxygen. The exit area of the torch tip ranges from that of aNo. 48 size orifice to that of a No. 30 size orifice with a No. 34 sizeproviding highly effective performance. A multiple orifice tip withthree No. 50 size orifices also provide highly effective performance.The aforementioned tip or orifice size numberscorrespond to those ofstandard U.S. twist drills. The flow rates of acetylene and oxygen aremade substantially equal to each other by the configuration of passagesfor them within the torch. The torch is thus operated under what isconventionally referred to as equal pressures to provide aneutraloxy-acetylene flame. The temperature of oxygen-acetylene flamesof varying proportions range from 5550 'F. to 6000 F., and a neutralflame has a temperature of approximately 5850 F.

With a No. 34 size tip upon a torch to which 9 p.s.i. of acetylene and28 p.s.i. of oxygen are applied, approximately 68 cubic feet per hour ofacetylene and 70 cubic feet per hour of oxygen are burned. With amultiple tip having three No. 50 size orifices, the corresponding flowrates of acetylene and oxygen are respectively 74 and 80 cubic feet perhour. Minimum effective flow rates of acetylene and oxygen within theindicated ranges of pressures and tip sizes are approximately 10 and 14c.f.h. Maximum effective flow rates of acetylene and oxygen within theindicated ranges of pressures and tip sizes are approximately 851 and100 c.f.h. At pressures of8-12 p.s.i. of acetylene and 2432 p.s.i. ofoxygen and a No.

34. size tip, approximately 6080 c.f.h. of acetylene and 60-90 c.f.h.of. oxygen are effective flow rates.

For supplying powder of the required particle size to a gas flameprovided by the aforementioned parameters, the diameter of a powderpassage of substantially circular cross section may vary fromapproximately 0.050 of an inch to 0.080 of an inch and preferably from0.065 to 0.075 an inch. Highly efficient powder flow is provided by asubstantially circular passageway having a 0.070 of an inch diameter.This provides a flow of metal powder to the aforementioned flame rangingapproximately from pounds per hour to pounds per hour with? an eflicientrange of 6 to 7 pounds per hour and ahighly efiicient rate of 6 /2pounds per hour.

The powders of this invention may have any composition that melts in therange between 360 F. and 2000" F. In the lower 360 F. to 1800 F. rangeare'found the metals and alloys (such as tin, lead, silver, antimony,cadmium, zinc and aluminum) that have relatively high vaporpressureswhich make them susceptible to volatilization-at normalflame-spraying temperatures. Although the temperature of aneutraloxygen-acetylene flame is approximately 5850 F., the powder sprayedthrough it is not heated to that temperature because of their relativelygreat mass and short passage time within the flame.

Inthe'torch; of the aforementioned copending application for. US.Letters Patent, S.N. 297,844, filed July 26', 1963, they powder isentrained in the oxygen by gravity flow and the differential in pressurebetween-the low" pressure in the restrictedintroduction portion of theoxygen passage and the higher pressure in the powder container. Thepowder laden oxygen is then mixed with acetylene and the mixture burnedwhen it is discharged from the'tip. The powder accordingly flows in theburning stream of gases of the flame spray. The rapidity and force ofthe flame spray helps coalesce the heated par ticles withthe preheatedmetal surface. This coalescence is facilitated by the pool of moltenmetal deposited by previously impinged particles that spreads over thesurface: of the preheated metal surface. Even though the sprayedparticles are so large and massive that they are: merelyplasticizedduring. their transit through the ame spray, the force of impingementand dissolution in the previously deposited molten pool effectivelybonds them to the preheated metal surface and coalesces them therewith.All'of, these factors cooperate with each other to form a smooth metalcoating upon a. preheated metal surfacedespite the relatively great massof the particles ofthis invention which previously would have beenconsidered too large to allow sufficient heating to bond them with ametal surface through flame spraying. These relatively massive particlesare so little affected by the heat that plasticize-d. them that nodiscernable volatilization occurs of compositions having meltingtemperatures from 360 to 2000 F. This avoids the serious fuming problem'associated with more volatile metals, suchas tin, lead, antimony, zincandJcadmium and for the first time makes it possible'to flame spraycompositions including them without any danger of poisoning. Othervolatile metalsisuch as aluminum may also be flame sprayed without anytoxic effects. or loss from the ultimate deposit.-

A composition that can be flame sprayed with remarkable-eifectivenessand absence of fuming through this invention isasilver base alloy havinga solidus temperature of 1125 F. The composition ofsuchpa silver basealloy is for example an AWS BAg-1 type as describedin the Brazing Manualof the American Welding Society, Inc., copyright 1963, and in AWSSpecification for Brazing Filler Metals, AWS A--5.8, ASTM B260. Allalloys designated herein as AWS refer to the aforementionedpublications.

Thisopens upthe field. of spraying to a wide variety of silver solderand silver brazing alloys that contain volatile constituents such aszinc and cadium whose loss would seriously detract from the physicalproperties of the ultimately deposited coating and whose fumes aretoxic. The same applies to soft solders of the tin/ lead type having asolidus of 361 F. and to tin/zinc systems having a solidus of 390 F.Other lower melting range systems can also be flame sprayed withremarkable absence of volatilization. These include the following havingthe indicated solidus temperatures: tin/ antimony 452 F., tin/silver 430F., lead/silver 579 F., cadium/ silver 640 F., cadium/zinc 509 F. andzinc/ aluminum 720 F.

A typical brass alloy that is flame deposited with complete carryover ofall constituents and with lack of fuming of this invention has forexample an AWS BCu Zn A type composition.

Despite the great susceptibility of zinc to fuming, the abovecomposition is totally flame deposited by this invention Without anyappreciable loss of zincor significant emission of its poisonous fumes.

As previously discussed, this invention is also quite advantageous forhigher melting temperature powders between 1800 and 2200 F. to completethe overall applicable range of 360 F. to 2200 F. This invention.

makes these high melting powders. insensitive to the effect of powderdistribution and configuration. With heretofore used powders of finerparticle size, a particular particle distribution had tobe maintainedvery carefully throughout the range from 150 through 325 mesh. This wasconsidered mandatory for suflicient heating and melting during flamespraying. It was also thought critical that the powder configuration bemaintained sub.- stantially spherical. This invention makes eflicientflame spraying insensitive to both particle size distribution andconfiguration.

A typicalnickel base alloy having a melting temperature of between 1800"F. and 2000 F. is. an AWS BNi2 type composition. Cobalt base alloysincorporating nickel and chronium constituents melt between 2000 F. and2200 F. and also are flame sprayed in accordance with this inventionwith remarkable effectiveness.

The effectiveness of this invention in flame spraying.

and particularly its elimination of fuming when spraying alloys that arehighly susceptible to fuming is highly remarkable in view of theinability of all previous modes of flame spraying to minimize fuming letalone completely. eliminate it. Even when finer powders are propelled atrelatively high velocities through a flame spray, such as by acompressed air propellant, substantial fumingstill: occurs. It is thushighly remarkable that powder compositions having relatively low meltingtemperatures :and whichare highly susceptible to volatilization do-notfume to any significant. extent.

What is claimed is:

1. Amethod. of flame spraying metal powders that minimizes the effect ofparticle size distribution and configuration and any tendency ofthepowder composition to volatilize comprising the selection of a metalpowder. compositionhaving a melting temperature ranging approximatelyfrom 360 F. to 2200 F., maintaining the particle size of said powderless than 40 mesh andapproximately 100% by weight thereof approximatelyfrom -60 to mesh, preheating said metal surface approximately to itsbonding temperature with said heated metal powders whereby coalescencetherewith is achieved, and flame spraying saidpowdered metal upon.

said metal surface within an oxy-fuel gas flame to plasticize saidpowdered metal without volatilizing it and to impinge it upon saidpreheated metal surface whereby it.

coalesces and bonds therewith to form a smooth continuous coating uponsaid metal surface.

2. A method asset forth in claim 1 wherein a metal powder composition isselected that has a meltingtemperature ranging approximately from 360 F.to 1800 F.

wherein many of said compositions are highly susceptible" tovolatiiizing when heated during passage within a flame spray, and saidmethod preventing said compositions from volatilizing and fuming wherebyloss of constituents and emission of toxic fumes during flame sprayingare avoided.

3. A method as set forth in claim 1 wherein said oxyfuel gas flameincorporates a burning mixture of a combustible gas and oxygen issuingto atmosphere from a torch to which they are supplied under pressure,said combustible gas being supplied at a pressure ranging approximatelyfrom 2 to 14 p.s.i., said oxygen being supplied at a pressure rangingapproximately from 16 to 50 psi, the exit area of said torch rangingapproximately from that provided by a No. 48 to a No. 30 tip size, andsaid powder flowing at a rate ranging approximately from 5 lbs. to lbs.per hour.

4. A method as set forth in claim 3 wherein the temperature of saidflame ranges approximately from 5550" F. to 6000 F.

5. A method as set forth in claim 3 wherein said powder is entrainedwithin said burning mixture and flows at substantially equal velocitytherewith within said flame toward said metal surface.

6. A metal powder for flame spraying that is relatively insensitive toparticle size and distribution and has a minimum tendency to volatilizecomprising a metal composition having a melting temperature ranging from360 F. to 2200 F., and the particle size of said powder ranging from 40to +140 mesh.

7. A metal powder as set forth in claim 6 wherein the meltingtemperature of said composition ranges from 360 F. to 1800 F.

8. A method as set forth in claim 3 wherein said combustible gas andsaid oxygen respectively flow at rates ranging from 10-88 and 14100cubic feet per hour.

9. A method as set forth in claim 1 wherein said particle size of saidpowder is distributed in the following ranges of percent by weight ofsaid powder:

Mesh-- Percent by wt.

References Cited UNITED STATES PATENTS 3,055,769 9/1962 Herron et al.1l746 X 3,071,678 1/1963 Neely et a1.

3,077,659 2/1963 Holzwarth et al. 29197 3,091,029 5/1963 Davis et al117105 X 3,285,769 11/1966 Cape 117 22 3,318,730 5/1967 Kreiselrnaier117--105 X ALFRED L. LEAVITT, Primary Examiner.

I. H. NEWSOME, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,372,054. March 5, 1968 Frederick T. Wishnie et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 35, for "3,220,068" read 3,226,028

Signed and sealed this 15th day of July 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, IR.

1. A METHOD OF FLAME SPRAYING METAL POWDERS THAT MINIMIZES THE EFFECT OFPARTICLE SIZE DISTRIBUTION AND CONFIGURATION AND ANY TENDENCY OF THEPOWDER COMPOSITION TO VOLATILIZE COMPRISING THE SELECTION OF A METALPOWDER COMPOSITION HAVING A MELTNG TEMPERATURE RANGING APPROXIMATELYFROM 360*F. TO 2200*F., MAINTAINING THE PARTICLE SIZE OF SAID POWDERLESS THAN 40 MESH AND APPROXIMATELY 75-100% BY WEIGHT THEREOFAPPROXIMATELY FROM -60 TO +100 MESH, PREHEATING SAID METAL SURFACEAPPROXIMATLEY TO ITS BONDING TEMPERATURE WITH SAID HEATED METAL POWDERSWHEREBY COALESCENCE THEREWITH IS ACHIEVED, AND FLAME SPRAYING SAIDPOWDERED METAL UPON SAID METAL SURFACE WITHIN AN OXY-FUEL GAS FLAME TOPLASTICIZE SAID POWDERED METAL WITHOUT VOLATILIZING IT AND TO IMPING ITUPON SAID PREHEATED METAL SURFACE WHEREBY IT COALESCES AND BONDSTHEREWITH TO FORM A SMOOTH CONTINUOUS COATING UPON SAID METAL SURFACE.